I totally agree with DLRExpert that In-N-Out is best for people who like the toppings and sauce on their burgers. We eat there sometimes because they are allergy friendly, if boring to those of us with allergies. DH loves the burgers, though. I just wish they had mayo.
Plenty of people prefer The Habit, or Five Guys. Both cost a lot more than In-N-Out. Almost twice as much. Five Guys is almost as expensive as eating at Red Robin, which is a sit down restaurant.
One thing to know, is that the patties are tiny, only 2 ounces each. My teens prefer to ask for a triple.
If you can eat the bun, the buns at In-N-Out are far better than most fast food places.
The fries aren't double-fried like most places, and again, are far better if you like them with ketchup or animal sauce. They aren't soaked in cold water to remove some starch before frying. They aren't like most fast food fries and I would say they are an acquired taste. You can also order cheese fries and they will put a couple of slices of cheese on an order of fries and then put it in the toaster oven to melt the cheese.
The shakes are pretty good

Usually very thick. You can mix the flavors, including get a Neapolitan.
In-N-Out is one of the few fast food places you can get 7Up at the soda fountain.
I don't think I would ever choose to walk to In-N-Out from the parks though.